This invention relates to coated abrasive products, and, in particular, to coated abrasive products having a radiation curable binder.
Coated abrasives generally comprise a backing and abrasive granules supported thereby and adhered thereto. The backing may be paper, cloth, polymeric, film, vulcanized fiber, etc. or a combination of two or more of these materials. The abrasive granules may be formed of flint, garnet, aluminum oxide, alumina-zirconia, diamond, silicon carbide, etc. Binders for the purpose of adhering the granules to the backing include phenolic resins, hide glue, varnish, epoxy resins, urea-formaldehyde resins, and polyurethane resins.
The coated abrasive may employ a "make" coat of resinous binder material which is utilized to secure the ends of the abrasive granules onto the backing as the granules are oriented and a "size" coat of resinous binder material over the make coat which provides for firm adherent bonding of the abrasive granules. The size coat resin may be of the same material as the make coat resin or it may be of a different resinous material.
In the manufacture of conventional coated abrasives, the make coat resinous binder is first applied to the backing, the abrasive granules are then applied, the make coat is partially cured, the size coat resinous binder is then applied, and finally, the construction is fully cured. Generally, thermally curable binders provide coated abrasives having excellent properties, e.g. heat resistance. Thermally curable binders include phenolic resins, epoxy resins, and alkyd resins. With backings formed of polyester or cellulose, however, curing temperatures are limited to a maximum of about 130.degree. C. At this temperature, cure times are sufficiently long to necessitate the use of festoon curing areas. Festoon curing areas are disadvantageous in that they result in formation of defects at the suspension rods, inconsistent cure due to temperature variations in the large festoon ovens, sagging of the binder, and shifting of abrasive granules. Furthermore, festoon curing areas require large amounts of space and large amounts of energy. Accordingly, it would be desirable to develop a resin that does not require a great deal of heat to effect cure. Radiation curable resins are known in the art. Offenlegungsschrift No. 1,956,810 discloses the use of radiation for the curing of unsaturated polyester resins, acid hardenable urea resins, and other synthetic resins, especially in mixtures with styrene as binder for abrasives. U.S. Pat. No. 4,047,903 discloses a radiation curable binder comprising a resin prepared by at least partial reaction of (a) epoxy resins having at least 2 epoxy groups, e.g. from diphenylolpropane and epichlorohydrin, with (b) unsaturated monocarboxylic acids, and (c) optionally polycarboxylic acid anhydride. U.S. Pat. No. 4,457,766 discloses the use of acrylated epoxy resins, which are designated therein "epoxy acrylates", such as the diacrylate esters of bisphenol A epoxy resins, as a radiation curable binder for coated abrasives.
The coated abrasives described in the foregoing patents exhibit the shortcoming of poor adhesion of abrasive granules to the backing because the binder does not cure in areas where the granules screen out radiation, unless high dosages of ionizing radiation are employed. High dosages of radiation can adversely affect the backing. The poor adhesion of the abrasive granules results in a large loss of abrasive granules, i.e. "shelling", from the backing upon flexing and grinding. Attempts to improve the adhesion of the abrasive granules by curing by ionizing radiation, e.g., electron beam, through the backside of the backing often leads to degradation of the backing.